Distance measuring devices in the vehicle, which determine the distance of a vehicle from an obstacle by emitting a transmitted signal and receiving the signal reflected from the obstacle, are known. Control of devices outside the vehicle such as entrance gates, garage doors, or barriers using portable wireless devices taken by a driver of a vehicle into the vehicle and actuated in front of a gate for opening and/or closing the gate, for example, is furthermore known. German Patent Application No. DE 41 23 640 describes a remote control device for a garage door drive, in which a car radio antenna is used as a transmitting antenna for the transmitter instead of such a hand-held transmitter. In this case, a diplexer is provided which is used for separating the radio signals and the transmitted signals.